Pregnancy Due Date Calculator

Find your due date from your last period, conception date or ultrasound, see how many weeks pregnant you are today, your trimester and the key dates.

First day of your last period

Average cycle length (days)

I also have an ultrasound (optional)

ℹ️ This is an estimate. Only about 1 in 20 babies is born on the due date itself, and most arrive within two weeks of it. Your doctor or midwife confirms the dates.

What it does

The due date is an estimate of the day the baby should arrive, 40 weeks after the first day of the last period. This calculator finds it from your last period (adjusted to your cycle length), from a known conception date or from an ultrasound, and shows how many weeks and days pregnant you are today, the trimester, and a timeline with the usual exam windows and the 37, 39, 40, 41 and 42-week milestones. Nothing you type leaves your browser.

How to use it

Choose how to calculate: from your last period, the conception date or an ultrasound.
Enter the date and, for the last period, your average cycle length. If you had an ultrasound, add its date and the age it measured.
See the due date, how far along you are today and the timeline with the key dates.

The arithmetic runs in your browser. Nothing you type is sent anywhere and nothing is stored, so you can use these with real numbers.

Frequently asked questions

How is the due date calculated?
Pregnancy is counted from the first day of the last period, not from conception, and the due date is 280 days (40 weeks) later: this is Naegele's rule. If your cycle is longer or shorter than 28 days, ovulation shifts, and the due date moves by the same number of days.

Why can an ultrasound change the due date?
An early ultrasound measures the baby and is usually more precise than the date of the last period. Following ACOG guidance, the date changes only when the difference exceeds a limit that grows with the pregnancy: 5 days up to 8 weeks, 7 days up to 15 weeks, 10 up to 21, 14 up to 27 and 21 days after that.

When does each trimester start?
The first trimester runs until 13 weeks and 6 days, the second from 14 weeks to 27 weeks and 6 days, and the third from 28 weeks until birth.

What do early term, full term, late term and post-term mean?
A baby born from 37 weeks is at term: early term from 37 weeks, full term from 39, late term from 41 and post-term from 42 weeks. A birth before 37 weeks is preterm.

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ACOG — Methods for Estimating the Due Date
Wikipedia — Estimated date of delivery